1. Technical Field
The embodiments herein generally relate to radio frequency (RF) and photonics, and more particularly to near-millimeter wave (NMMW), terahertz (TH), and microwave (MW) imaging for use in remote sensing (either active or passive, and especially through obscurants), security scanning, medical scanning, and related applications.
2. Description of the Related Art
Within the context of the embodiments herein, “RF” includes MW, NMMW, and TH radiation. By historical convention, these wavelengths are commonly referred to in the literature as RF, even though the wavelengths are much shorter than those used for radio.
Imaging systems may be active, meaning that they include a source of radiation other than the object being viewed. Commonplace examples of active imaging systems are x-ray machines and cameras with a flash. Imaging systems may also be passive, meaning that they utilize only ambient radiation coming from the object of interest. Commonplace examples are cameras and camcorders using only daylight, and infrared viewers for rifle sights, medical imaging, or satellite imagery.
RF active and passive imaging systems are complementary to visible light and infrared (IR) imaging because they encompass wavelength “windows” for transmission through fog, rain, and certain materials, and can be used day and night. Also, certain RF wavelengths may have absorption spectrum features for certain chemical or biochemical species. Therefore, RF imaging systems have important applications for the military, homeland security, civilian aviation, automobile safety, and medical diagnosis.
Generally, there have been a limited number of previously known RF imaging systems. Typically, these have been and are being developed with traditional radar technology that involves sophisticated and expensive electronic circuitry and systems. In addition, previously known systems have generally not proven wholly satisfactory in operation. An important restriction so far has been in the small number of pixels, which is due to the need in these previous systems to directly couple each pixel to a RF detector containing active circuitry to down-convert the very high frequency RF to a low frequency signal that can be handled with conventional electronics. These RF detectors tend to be expensive, heavy, and consume large amounts of electrical power. In fact, the production and operating costs of the RF detectors are such that most RF imaging systems must typically employ scanning techniques to enable them to produce images with only a one-dimensional (1D) array of detectors or even with only one detector. Accordingly, there remains a need for a relatively inexpensive and user-friendly RF imaging system.